Gangliosides and synaptosomal calcium homeostasis.

In this study, depolarization-dependent (net) calcium transport and binding capacity to rat brain synaptosomes was investigated under conditions affecting the ganglioside composition of the synaptoplasmatic membranes. Specific interaction of the monosialoganglioside GM1 with the membrane, as observed in low (40 nM) concentration of ganglioside, resulted in significant inhibition of the maximal depolarization-induced calcium uptake. The changes in ganglioside composition of synaptosomes produced by N-ase treatment did not affect the maximal net Ca++ uptake. However both procedures resulted in the decrease of calculated half-time of the depolarization-induced calcium influx. Exposure of synaptosomes either to GM1 in 40 nM concentration or to N-ase led to a significant drop in 45Ca++ binding to the membrane and increase in the CTC-Ca++ fluorescence. The results suggest that gangliosides are potent modulators of synaptosomal calcium fluxes and equilibration in the membrane.